Colorado River Cutthroat Trout
Colorado River Cutthroat Trout (Photo by Ron Stewart)

Biologists from the Utah Division of Wildlife Resources (DWR) have discovered the parasite that causes Whirling Disease in fish taken from the Duchesne River. Samples collected recently from the confluence of the West and North Forks, and approximately three miles downstream of Tabiona, tested positive for the pathogen. In addition, Whirling Disease was confirmed in Rock Creek, a tributary to the Duchesne, several miles below the Stillwater Ponds.

This marks the first time Whirling Disease has been found in the Uinta Basin or Duchesne/Strawberry River drainage, and the fourth time in the Northeastern Region. The other hot spots are Carter Creek from Brownie Lake to Flaming Gorge Reservoir, Burnt Fork Creek east of Flaming Gorge, and Long Park Reservoir.

What happens now?

"Whirling Disease is caused by a small parasite that attacks the cartilage of a trout or salmon's head and spine," Schneidervin said. "If significantly infected, a fish can exhibit the whirling behavior (swimming in circles) and could die. Diseased fish have more problems swimming, are easier prey for predators, and become more susceptible to other diseases and environmental stress.

"In some Western waters, the disease has caused major impacts to wild rainbow and cutthroat trout fisheries. For example, some of the more productive reaches of the famous Madison River in Montana have had wild trout populations decline by up to 90 percent. In other streams, the parasite has had no apparent impact. It particularly affects young fish in naturally reproducing populations. Adult fish may become infected, but often don't exhibit signs of the disease." (Note: the Whirling Disease parasite does not infect humans.)

The discovery in the Duchesne River is of major concern to DWR biologists.

"Although the lower Duchesne is primarily a wild brown trout fishery, a species naturally more resistant to the disease, the upstream reaches of the river contain stocked rainbow and wild cutthroat trout," Schneidervin said. "Of particular concern is an invaluable population of pure strain Colorado River cutthroat trout located above the Central Utah Project (CUP) VAT Diversion on the West Fork. These fish are the source of the brood population in Sheep Creek Lake that provides eggs for intensive conservation efforts to prevent these native fish from being listed as Threatened or Endangered."

Schneidervin is also concerned about the location of the infection.

"Besides infecting this pure strain Colorado River cutthroat trout population and compromising one of the Region's premiere Blue Ribbon trout streams, if the pathogen gets above the CUP diversion system, it will rapidly spread to Currant Creek, Strawberry Reservoir, Diamond Fork and the Spanish Fork River by the CUP transfer tunnels."

What can be done?

"The good news is that trout populations upstream on both the Duchesne River and Rock Creek were subsequently tested and found negative for the disease," Schneidervin said. "We're now working with the Uinta and Ashley National Forests to create a secondary fish barrier (like a dam or waterfall) below the VAT Diversion, place signs to alert and educate anglers, and initiate additional sampling to define the extent of the infection and identify hot spots regarding the potential spread of the pathogen above the CUP diversions."

"We also need help from anglers to prevent movement of the disease above the barriers or to additional waters," Schneidervin said. "The parasite has a complex life cycle. It starts as a spore (like a small microscopic egg) released from an infected fish. A small aquatic worm ingests the spore, where the parasite changes and is released as a free-swimming form. This "myxospore" enters a fish through the gills or skin and migrates through the nervous system, typically finding its way to the cartilage of the head or spine. Once in the fish, it starts producing spores. When the fish dies, the spores are released into the water where they can survive in the sediment for years before a worm ingests them and starts a new cycle.

"It's critical that anglers avoid harvesting fish in one area, then transporting their catch to another location to clean them," Schneidervin said. "Anglers who camp in one area and fish in another must be especially diligent. Because a single fish can contain thousands or even millions of spores, this mechanism [anglers moving fish and fish parts] may be responsible for many of the recent Whirling Disease introductions. Please clean fish well away from the water and dispose of all fish parts including entrails, heads, skeletons, etc. in the garbage. If that isn't possible, bury the parts deeply or burn them completely."

"Anglers and others who wade in the stream or get mud on boots, vehicle tires, or equipment can also move spores by carrying that mud to another site," Schneidervin said. "The best defense is to carefully clean all waders, boats, trailers, float tubes, etc. before reuse in another water. Anglers are also encouraged to use wading shoes that do not have felt soles, which are much more difficult to clean. Felt soles are also believed to be a major cause of the movement of New Zealand Mud Snails.

"Gear can be washed in a 10 percent solution of chlorine bleach, then dried thoroughly, preferably in the sun. Remember to drain and dry holding tanks and bilge pumps so fish and other uninvited guests, like Whirling Disease, New Zealand Mud Snails or Zebra Mussels, don't get moved with the water from one place to another."

"There is no cure for Whirling Disease and once introduced into a watershed the disease cannot be eliminated," Schneidervin concluded. "We are highly concerned about the parasite infecting major fisheries and the lakes, rivers and tributary streams in the Uintas and other mountains. It could seriously reduce our native and wild populations of cutthroat and rainbow trout. For the angler it may mean lower catch rates for many others it's a serious blow to their quality of life. We need everyone's help to stop the spread of this disease and protect these invaluable Utah fisheries."

by Ron Stewart, Utah Division of Wildlife Resources